This proposal deals with interdisciplinary studies (in biochemistry, immunology and hematology) aimed at increasing our knowledge of the primitive nurse shark immune system in hopes of better understanding the complex immune system found in mammals. The nurse shark immune system has not been extensively studied and is poorly understood. While it is known that shark plasma contains an iron-binding protein similar to human serum transferrin (TF), it has long been assumed that lactoferrin (LF), a similar iron- binding protein originally discovered in mammalian milk, is found only in mammals. It is widely assumed that transferrin and lactoferrin diverged from a common precursor in early mammalian evolution. In the past decade, lactoferrin has been extensively investigated and found to occur widely in mammals in body fluids and in secondary granules of polymorphonuclear (PMN) cells where it has been shown to act as a negative feedback inhibitor of granulocyte/macrophage colony stimulating factor (GM-CSF) produced by monocytes/macrophages. The presence/absence of LF-like protein in shark leukocytes could possibly shed light on the complex immunomodulatory role that lactoferrin plays in mammals. Chemical, immunological and microscopic methods will be utilized to investigate whether shark leukocytes contain iron-binding proteins similar to lactoferrin and to determine whether LF-like proteins are able to bind to shark leukocytes. Lack of evidence for tumor formation in the nurse shark has led investigators to suggest that this primitive animal may possess some type of antitumor activity. For this reason, proposed studies of the nurse shark immune system also include a preliminary search for the presence of antitumor factors. Antineoplastic activity of cell-free shark leukocyte lysates and heat-inactivated serum and/or serum fractions will be investigated using human and mouse tumor cell lines. Finally, an attempt will be made to establish an in vitro shark cell culture from peripheral blood leukocytes and to subsequently demonstrate cytotoxic activity in cell culture supernatants.